1. Field of the Invention
The present invention relates to transmission lines in which signal conductors are located close to one another and transmit different high frequency signals.
2. Description of the Related Art
Various types of transmission lines transmit high frequency signals. For example, a transmission line described in Japanese Patent No. 4962660 includes a stripline structure. The transmission line described in Japanese Patent No. 4962660 includes an elongated dielectric base body extending in a transmission direction of high frequency signals, a signal conductor, and a first ground conductor, and a second ground conductor. The signal conductor is located at a midway position in a thickness direction of the dielectric base body. The signal conductor is located between the first ground conductor and the second ground conductor in the thickness direction, that is, a stacking direction, of the dielectric base body. Furthermore, the first ground conductor and the second ground conductor are connected to each other via a plurality of via-hole conductors arranged along the signal conductor. Accordingly, a transmission line including a stripline structure with a signal conductor located between first and second ground conductors is provided.
For example, if a plurality of transmission lines as described in Japanese Patent No. 4962660 are located close to one another in a communication device or the like, a plurality of signal conductors are likely to be located on a single dielectric base body. Accordingly, the plurality of signal conductors may be spaced from each other in a direction orthogonal or substantially orthogonal to the thickness direction of the dielectric base body and a signal transmission direction.
In a transmission line in which a dielectric base body includes a single unit defined by arranging and connecting transmission lines each including the structure described in Japanese Patent No. 4962660 to each other in a width direction of the dielectric base body, interlayer connection conductors located between the signal conductors significantly reduces or prevents coupling between signal conductors that are adjacent to or in a vicinity of one another.
In the configuration described above in which interlayer connection conductors are arranged between signal conductors that are adjacent to or in a vicinity of one another, however, a reduction in the number of interlayer connection conductors or a removal of interlayer connection conductors may result in the signal conductors being likely to be coupled to each other. In contrast, an increase in the number of interlayer connection conductors may cause unnecessary coupling to be likely to occur between the signal conductors and the interlayer connection conductors, making it difficult to achieve a desired impedance of a transmission line. In particular, a reduction in the width of the dielectric base body further results in it being more difficult to significantly reduce or prevent unnecessary coupling between the interlayer connection conductors and the signal conductors.
Moreover, the arrangement of interlayer connection conductors between signal conductors does not facilitate a reduction in the width of the dielectric base body.